1. Field of the Invention
The present invention relates to an image forming process such as electrophotography, electrostatic recording, and electrostatic printing, in particular, to an image forming process which employs non-magnetic one-component type developer, and also relates to an image forming apparatus, an apparatus unit, and a facsimile apparatus.
2. Related Background Art
Many electrophotographic processes are already known as described in U.S. Pat. No. 2,297,691, and Japanese Patent Publication Nos. 42-23910 and 43-24748. Generally in these methods, an electric latent image is formed on a photosensitive member by utilizing a photoconductive substance and developed with a toner, and then, the toner image is transferred if necessary onto an image-receiving medium like paper, and fixed by heating, pressing, hot-pressing, or solvent-vapor treatment to obtain a copy. The untransferred toner which remained on the photosensitive member was cleaned, and the above steps are repeated.
In recent years, such types of copying apparatuses have come into use not only for business copying machines for copying an original but also for printers for output of computers, and personal copying machines.
For this reason, such properties as compact size, light weight and small power-consumption are required for copying apparatus. Consequently, copying apparatus has come to consist of simpler elements in many respects. To developed electrostatic latent images, two-component developing methods and one-component developing methods are known widely. In the two-component developing methods, a mixture of a toner and a carrier is used, and in the one-component developing methods, a magnetic toner only is used. The two-component developing method cannot meet the requirements for smaller size and light weight because it employs a carrier and an ATR mechanism for controlling the mixing ratio of the toner and the carrier is necessary. The one-component developing methods have disadvantages owing to difficulty in application to color toners because the methods use a magnetic toner.
On the other hand, Japanese Laid-Open Patent Application Nos. 58-116559, 60-120368, and 63-271371 disclose non-magnetic one-component developing methods which is a noteworthy method to solve the above problems.
In the non-magnetic one-component developing methods, a developer is applied on a developer-carrying member by use of a layer thickness-controlling means such as a blade. The developer is electrostatically charged by the friction with the blade or the surface of the developer-carrying member. However, if the applied layer of the developer is excessively thick, some portion of the developer is not sufficiently electrically charged, which may cause fogging or black spots around the line image. Therefore, the developer should be applied in a thin layer. For this reason, the blade has to be pressed against the developer-carrying member with a sufficiently large pressure, thereby the developer receives greater force than the developer in a two-component developing method or a one-component developing method employing a magnetic toner. Thus, in such a method, the developer is liable to deteriorate, causing poor image quality such as fogging or low density.
The developer employed for a non-magnetic one-component developing method is required to have a high mechanical strength and a high thermal strength. However, if these strengths are simply increased, they result in increase of the heat energy consumed for fixation, which is contrary to the low power-consumption requirement.
As described above, further improvement is required for the non-magnetic one-component developing method to achieve high developability, fixability, and anti-offset property.